Field of the Invention
The present invention relates to a worm gear applicable to a reducer of member opened or closed by power, and, for example, to a worm gear of a reducer used to open or close a power window or a sunroof of a vehicle.
Description of the Related Art
Motors provided with a reducer including a worm and a worm wheel are conventionally known as a mechanism to drive the power window of a vehicle. Normally, a gear mesh between a worm and a worm wheel is filled with a lubricant such as grease in order to reduce abrasion between teeth.
It is desirable that the lubricant remain in the gear mesh for a long period time and even in the presence of a change in the environment in which the lubricant is used. For example, there is proposed a worm having a tooth face with a recess for retaining a lubricant (see patent document 1). The document describes the worm in which such a configuration is employed as being characterized by improved lubrication between tooth faces and reduced abrasion on the tooth faces pressed into contact with each other as the worm and the worm wheel mesh with each other.
[patent document 1] JP2003-65422
When the motor is not driven, grease is located evenly on the right side and on the left side of the tooth of the worm wheel. The motor repeats normal rotation (CW) or reverse rotation (CCW) depending on the use. For this reason, “the right side of the tooth of the worm” and “the left side of the tooth of the worm wheel” are in contact with each other as the motor is driven to a reverse rotation. As a result, the thickness of the grease in this part of the assembly will be reduced. The grease will flow from where its thickness is reduced toward “the right side of the tooth of the worm wheel” via the grease pool of the worm gear. On the other hand, when the motor is driven to a normal rotation, “the left side of the tooth of the worm” and “the right side of the tooth of the worm wheel” are in contact with each other. As a result, the thickness of the grease in this part of the assembly will be reduced. The grease will flow from where its thickness is reduced toward “the left side of the tooth of the worm wheel” via the grease pool of the worm gear.
Normally, a suitable backlash exists between “the tooth of the worm” and “the tooth of the worm wheel”. Therefore, the flow of grease as described above can be maintained. However, depending on the condition or environment in which the motor is used, the backlash may be reduced, the volume of grease may be reduced, or the quality of the grease may become poor so that the proper flow of grease may not be maintained.